4,579 research outputs found
Combustion instability prediction using a nonlinear bipropellant vaporization model
Combustion instability prediction using nonlinear bipropellant vaporization mode
Simultaneous interplanetary scintillation and Heliospheric Imager observations of a coronal mass ejection
We describe simultaneous Interplanetary Scintillation (IPS) and STEREO Heliospheric Imager (HI) observations of a coronal mass ejection (CME) on 16 May 2007. Strong CME signatures were present throughout the IPS observation. The IPS raypath lay within the field-of-view of HI-1 on STEREO-A and comparison of the observations shows that the IPS measurements came from a region within a faint CME front observed by HI-1A. This front may represent the merging of two converging CMEs. Plane-of-sky velocity estimates based on time-height plots of the two converging CME structures were 325 kms?1 and 550 kms?1 for the leading and trailing fronts respectively. The plane-of-sky velocities determined from IPS ranged from 420 ± 10 kms?1 to 520 ± 20 kms?1. IPS results reveal the presence of micro-structure within the CME front which may represent interaction between the two separate CME events. This is the first time that it has been possible to interpret IPS observations of small-scale structure within an interplanetary CME in terms of the global structure of the event
Higher-dimensional Algebra and Topological Quantum Field Theory
The study of topological quantum field theories increasingly relies upon
concepts from higher-dimensional algebra such as n-categories and n-vector
spaces. We review progress towards a definition of n-category suited for this
purpose, and outline a program in which n-dimensional TQFTs are to be described
as n-category representations. First we describe a "suspension" operation on
n-categories, and hypothesize that the k-fold suspension of a weak n-category
stabilizes for k >= n+2. We give evidence for this hypothesis and describe its
relation to stable homotopy theory. We then propose a description of
n-dimensional unitary extended TQFTs as weak n-functors from the "free stable
weak n-category with duals on one object" to the n-category of "n-Hilbert
spaces". We conclude by describing n-categorical generalizations of deformation
quantization and the quantum double construction.Comment: 36 pages, LaTeX; this version includes all 36 figure
EISCAT measurements of solar wind velocity and the associated level of interplanetary scintillation
International audienceA relative scintillation index can be derived from EISCAT observations of Interplanetary Scintillation (IPS) usually used to study the solar wind velocity. This provides an ideal opportunity to compare reliable measurements of the solar wind velocity derived for a number of points along the line-of-sight with measurements of the overall level of scintillation. By selecting those occasions where either slow- or fast-stream scattering was dominant, it is shown that at distances from the Sun greater than 30 RS , in both cases the scintillation index fell with increasing distance as a simple power law, typically as R-1.7. The level of scintillation for slow-stream scattering is found to be 2.3 times the level for fast-stream scattering
Epicardial adiposity in people with atrial fibrillation modified by physical exercise: an umbrella review
Principal 2-bundles and their gauge 2-groups
In this paper we introduce principal 2-bundles and show how they are
classified by non-abelian Cech cohomology. Moreover, we show that their gauge
2-groups can be described by 2-group-valued functors, much like in classical
bundle theory. Using this, we show that, under some mild requirements, these
gauge 2-groups possess a natural smooth structure. In the last section we
provide some explicit examples.Comment: 40 pages; v3: completely revised and extended, classification
corrected, name changed, to appear in Forum Mat
Catalysis study for space shuttle vehicle thermal protection systems
Experimental results on the problem of reducing aerodynamic heating on space shuttle orbiter surfaces are presented. Data include: (1) development of a laboratory flow reactor technique for measuring gamma sub O and gamma sub N on candidate materials at surfaces, T sub w, in the nominal range 1000 to 2000, (2) measurements of gamma sub O and gamma sub N above 1000 K for both the glass coating of a reusable surface insulation material and the siliconized surface of a reinforced pyrolyzed plastic material, (3) measurement of the ablation behavior of the coated RPP material at T sub w is greater than or equal to 2150 K, (4) X-ray photoelectron spectral studies of the chemical constituents on these surfaces before and after dissociated gas exposure, (5) scanning electron micrograph examination of as-received and reacted specimens, and (6) development and exploitation of a method of predicting the aerodynamic heating consquences of these gamma sub O(T sub w) and gamma sub N(T sub w) measurements for critical locations on a radiation cooled orbiter vehicle
Accurate OH maser positions II. the Galactic Center region
We present high spatial resolution observations of ground-state OH masers,
achieved using the Australia Telescope Compact Array (ATCA). These observations
were conducted towards 171 pointing centres, where OH maser candidates were
identified previously in the Southern Parkes Large-Area Survey in Hydroxyl
(SPLASH) towards the Galactic Center region, between Galactic longitudes of
and and Galactic latitudes of and
. We detect maser emission towards 162 target fields and suggest
that 6 out of 9 non-detections are due to intrinsic variability. Due to the
superior spatial resolution of the follow-up ATCA observations, we have
identified 356 OH maser sites in the 162 of the target fields with maser
detections. Almost half (161 of 356) of these maser sites have been detected
for the first time in these observations. After comparing the positions of
these 356 maser sites to the literature, we find that 269 (76\%) sites are
associated with evolved stars (two of which are planetary nebulae), 31 (9\%)
are associated with star formation, four are associated with supernova remnants
and we were unable to determine the origin of the remaining 52 (15\%) sites.
Unlike the pilot region (\citealt{Qie2016a}), the infrared colors of evolved
star sites with symmetric maser profiles in the 1612 MHz transition do not show
obvious differences compared with those of evolved star sites with asymmetric
maser profiles.Comment: 24 pages, 12 figures, accepted by ApJ
New class I methanol masers
We review properties of all known collisionally pumped (class I) methanol
maser series based on observations with the Australia Telescope Compact Array
(ATCA) and the Mopra radio telescope. Masers at 36, 84, 44 and 95 GHz are most
widespread, while 9.9, 25, 23.4 and 104 GHz masers are much rarer, tracing the
most energetic shocks. A survey of many southern masers at 36 and 44 GHz
suggests that these two transitions are highly complementary. The 23.4 GHz
maser is a new type of rare class I methanol maser, detected only in two
high-mass star-forming regions, G357.97-0.16 and G343.12-0.06, and showing a
behaviour similar to 9.9, 25 and 104 GHz masers. Interferometric positions
suggest that shocks responsible for class I masers could arise from a range of
phenomena, not merely an outflow scenario. For example, some masers might be
caused by interaction of an expanding HII region with its surrounding molecular
cloud. This has implications for evolutionary sequences incorporating class I
methanol masers if they appear more than once during the evolution of the
star-forming region. We also make predictions for candidate maser transitions
at the ALMA frequency range.Comment: 8 pages, 2 figures, to appear in proceedings for IAUS 287: Cosmic
Masers - from OH to H
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